Traditional VoD is based on a client-server approach, which is expensive and not scalable. In recent years, the P2P approach was first demonstrated to work for a live content streaming, and later for a VoD streaming as well. Various efforts are working on building a P2P-based VoD platform, for example using set-top boxes (STBs).
The VoD streaming is definitely harder to be accomplished than the live content streaming, since peers are less likely to have the same contents to share with each other. The lack of synchrony (in VoD) is compensated by following two remedial features in P2P VoD systems: a) each peer contributes more storage to replicate the VoD contents; and b) each peer is capable of uploading the contents different from what is currently consumed (downloaded) locally. The effectiveness of this remedy depends on whether the right mix of the media contents is placed at different peers, which is the P2P replication problem at hand. The P2P replication is a central design issue in the P2P VoD systems.
The problem formulation is based on a requirement on more contemporary P2P VoD systems, where the majority of the peers expect to be streaming the contents for immediate viewing. In such systems, video servers must still be deployed to ensure the service quality. A P2P network may be viewed as a mechanism used to off-load the video servers. The objective is to minimize the server bandwidth while peers' viewing quality is ensured. The streaming requirement means there needs to be a balance between the total supply of uplink bandwidth (that is the sum of server(s) and peers' uplink bandwidth) and the total demand (that is the number of viewing peers multiplied by the video playback rate). In practice, the operating regime of particular interest is when the total peer uplink bandwidth is comparable to the demand (of viewing bandwidth). In this regime, ideally the server bandwidth may be zero, if the viewing demand is deterministically known, and all the peers are replicated with the right mix of the contents so as to make full use of their upload capacities. In reality, the impredicability of user demand, and thus the imperfection content replication and service load balancing will always result in some server load.
In addition, traditional VoD systems purely rely on servers to stream video content to clients, which does not scale. In recent years, P2P VoD has been proven to be practical and effective. In P2P VoD system, each peer (or a STB) contributes some storage to store video (or segments of video) content to help the video server. The present application refers to such content replications for P2P VoD applications that help the peers to make an optimal replication decision, i.e. to decide what contents should be replicated locally, so that their upload capacity can be utilized as much as possible under dynamic movie access rate/popularity conditions.